1. Field of the Invention
The present invention relates to a piezoelectric substance, a piezoelectric element, a liquid discharge head using the same, and a liquid discharge apparatus.
2. Description of the Related Art
In recent years, a piezoelectric actuator has been paid attention to at a point that miniaturization and high densification of a motor is possible, in a portable information device field, chemistry, and a medical field as a new motor which replaces an electromagnetic motor. The piezoelectric actuator does not generate an electromagnetic noise on the occasion of its drive, and, is not influenced by noise. Furthermore, the piezoelectric actuator attracts attention as technology of making such equipment with millimeter class size that is represented by a micromachine, and a minute piezoelectric element is requested as its drive source.
As for a piezoelectric element, generally, it is common to finely form and produce a sintered compact of a bulk material or a single crystal member, which is given heat-treatment to a piezoelectric substance, in desired size and thickness with technology such as machining and polishing. In addition, when forming a minute piezoelectric element, a method of directly forming a piezoelectric element by coating and sintering a green sheet-like piezoelectric substance by using methods, such as a printing method, in a predetermined position on a substrate, such as metal or silicon is common. A thickness of such a compact from a green sheet is tens to hundreds of micrometers, electrodes are provided in upper and lower sides of the piezoelectric substance, and a voltage is applied through the electrodes.
Heretofore, a small piezoelectric element which was used for a liquid discharge head was produced by finely forming a piezoelectric substance in a bulk material with technology such as machining or polishing as mentioned above, or using a green sheet-like piezoelectric substance. As a device using such a piezoelectric element, for example, there is a liquid discharge head which has unimorph type piezoelectric element structure. The liquid discharge head is equipped with a pressure chamber communicating with an ink feed chamber, and an ink ejection orifice communicating with the pressure chamber, and a vibrating plate with which the piezoelectric element is bonded or in which it is formed directly is provided and constructed in the pressure chamber. In such construction, an ink droplet is discharged from the ink discharge port by compressing the ink in the pressure chamber by generating deflection vibration, which is caused by expanding and contracting the piezoelectric element by applying a predetermined voltage to the piezoelectric element.
Although color ink jet printers have spread presently by using such an operation, enhancement in their printing performance, and in particular, higher resolution, and high speed printing are requested. Therefore, it has been attempted to attain high resolution and high speed printing using multi-nozzle head structure in which a liquid discharge head has been miniaturized. In order to miniaturize a liquid discharge head, it is necessary to miniaturize further a piezoelectric element for discharging ink. Furthermore, recently, attempts of applying liquid discharge heads to industrial applications such as straight-writing of wiring have been also active. At that time, it is necessary to pattern liquid with more various characteristics at higher resolution, and hence, further high performance of a liquid discharge head is requested.
In recent years, because of development of micromachine technology, researches of developing a highly precise micro piezoelectric element by forming a piezoelectric substance as a thin film, and using fine processing technology having been used in semiconductors have been performed. In particular, a thickness of a piezoelectric substance formed by film methods, such as a sputtering method, a chemical vapor deposition method, a sol gel method, and a gas deposition method is generally hundreds of nanometers to tens of micrometers in the case of an application to a piezoelectric actuator. Electrodes are provided on the piezoelectric substance and a voltage is applied through the electrodes.
On the other hand, research of high performance piezoelectric materials, having greater piezoelectric property, in connection with miniaturization of a piezoelectric element is also active. As a piezoelectric material which has attracted attention recently, there is a ferroelectric material which has the perovskite type structure which is constructed in a general formula ABO3. This material exerts excellent ferroelectricity, pyroelectricity, and piezoelectricity as represented, for example, by Pb(ZrxTi1-x)O3 (lead zirconate titanate: PZT).
When a piezoelectric element made of PZT is generally formed by a film method, such as a sputtering method, a chemical vapor deposition method, a sol gel method, or a gas deposition method, a thin film obtained takes the perovskite type structure which is constructed in the general formula ABO3. When the element ratio Pb/(Zr+Ti) of Pb, Zr and Ti is equal to or less than 1, which is a stoichiometric ratio of the perovskite type structure which is constructed in the general formula ABO3, piezoelectricity drops rapidly. For this reason, when forming the piezoelectric element made of PZT, Pb may be added a little more excessively than the stoichiometric ratio, and in particular, the sputtering method has that tendency remarkably. Nevertheless, when Pb is added further in excess of the stoichiometric ratio, generally a leakage current at the time of voltage application increases. For this reason, it was necessary to decide an optimum Pb excessive dosage with an effect of increase of leakage current, and piezoelectricity as trade-off relation. (Non-Patent Document 1: FUJITSU.53, 2, p. 105-109 (March, 2002)).
The present invention aims at providing a piezoelectric substance which solves the above-mentioned problems, has large piezoelectricity, and uses PZT, which can suppress a leakage current at the time of voltage application which becomes a problem at the time of lead excessive addition, as a main component, and a piezoelectric element using this. In addition, the present invention aims at providing a liquid discharge head, which exerts uniform and high discharging performance and can perform fine patterning, and a liquid discharge apparatus having this.